timestamp (Transact-SQL)
Is a data type that exposes automatically generated, unique binary numbers within a database. timestamp is generally used as a mechanism for version-stamping table rows. The storage size is 8 bytes. The timestamp data type is just an incrementing number and does not preserve a date or a time. To record a date or time, use a datetime data type.
Each database has a counter that is incremented for each insert or update operation that is performed on a table that contains a timestamp column within the database. This counter is the database timestamp. This tracks a relative time within a database, not an actual time that can be associated with a clock. A table can have only one timestamp column. Every time that a row with a timestamp column is modified or inserted, the incremented database timestamp value is inserted in the timestamp column. This property makes a timestamp column a poor candidate for keys, especially primary keys. Any update made to the row changes the timestamp value and, therefore, changes the key value. If the column is in a primary key, the old key value is no longer valid, and foreign keys referencing the old value are no longer valid. If the table is referenced in a dynamic cursor, all updates change the position of the rows in the cursor. If the column is in an index key, all updates to the data row also generate updates of the index.
You can use the timestamp column of a row to easily determine whether any value in the row has changed since the last time it was read. If any change is made to the row, the timestamp value is updated. If no change is made to the row, the timestamp value is the same as when it was previously read. To return the current timestamp value for a database, use @@DBTS.
The Transact-SQL timestamp data type is different from the timestamp data type defined in the SQL-2003 standard. The SQL-2003 timestamp data type is equivalent to the Transact-SQL datetime data type.
rowversion is the synonym for the timestamp data type and is subject to the behavior of data type synonyms. In DDL statements, use rowversion instead of timestamp wherever possible. For more information, see Data Type Synonyms (Transact-SQL).
In a CREATE TABLE or ALTER TABLE statement, you do not have to specify a column name for the timestamp data type, for example:
CREATE TABLE ExampleTable (PriKey int PRIMARY KEY, timestamp);
insert into ExampleTable(PriKey) values(1)
insert into ExampleTable(PriKey) values(2)
insert into ExampleTable(PriKey) values(3)
insert into ExampleTable(PriKey) values(4)
Select MAX(timestamp) from ExampleTable
update ExampleTable set PriKey =110 where PriKey =3
Select MAX(timestamp) from ExampleTable
If you do not specify a column name, the Microsoft SQL Server 2005 Database Engine generates the timestamp column name; however, the rowversion synonym does not follow this behavior. When you use rowversion, you must specify a column name.
Duplicate timestamp values can be generated by using the SELECT INTO statement in which a timestamp column is in the SELECT list. We do not recommend using timestamp in this manner.
A nonnullable timestamp column is semantically equivalent to a binary(8) column. A nullable timestamp column is semantically equivalent to a varbinary(8) column.
rowversion (Transact-SQL)
Is a data type that exposes automatically generated, unique binary numbers within a database. rowversion is generally used as a mechanism for version-stamping table rows. The storage size is 8 bytes. The rowversion data type is just an incrementing number and does not preserve a date or a time. To record a date or time, use a datetime2 data type.
Each database has a counter that is incremented for each insert or update operation that is performed on a table that contains a rowversion column within the database. This counter is the database rowversion. This tracks a relative time within a database, not an actual time that can be associated with a clock. A table can have only one rowversion column. Every time that a row with a rowversion column is modified or inserted, the incremented database rowversion value is inserted in the rowversion column. This property makes a rowversion column a poor candidate for keys, especially primary keys. Any update made to the row changes the rowversion value and, therefore, changes the key value. If the column is in a primary key, the old key value is no longer valid, and foreign keys referencing the old value are no longer valid. If the table is referenced in a dynamic cursor, all updates change the position of the rows in the cursor. If the column is in an index key, all updates to the data row also generate updates of the index.
timestamp is the synonym for the rowversion data type and is subject to the behavior of data type synonyms. In DDL statements, use rowversion instead of timestamp wherever possible. For more information, see Data Type Synonyms (Transact-SQL).
The Transact-SQL timestamp data type is different from the timestamp data type defined in the ISO standard.
In a CREATE TABLE or ALTER TABLE statement, you do not have to specify a column name for the timestamp data type, for example:
CREATE TABLE ExampleTable (PriKey int PRIMARY KEY, timestamp);
If you do not specify a column name, the SQL Server Database Engine generates the timestamp column name; however, the rowversion synonym does not follow this behavior. When you use rowversion, you must specify a column name, for example:
CREATE TABLE ExampleTable2 (PriKey int PRIMARY KEY, VerCol rowversion) ;
A nonnullable rowversion column is semantically equivalent to a binary(8) column. A nullable rowversion column is semantically equivalent to a varbinary(8) column.
You can use the rowversion column of a row to easily determine whether any value in the row has changed since the last time it was read. If any change is made to the row, the rowversion value is updated. If no change is made to the row, the rowversion value is the same as when it was previously read. To return the current rowversion value for a database, use @@DBTS.
You can add a rowversion column to a table to help maintain the integrity of the database when multiple users are updating rows at the same time. You may also want to know how many rows and which rows were updated without re-querying the table.